It is desirable in the background art of fuel systems to provide a manual bypass or override control function in order to provide backup or supplementary control of engine fuel systems during or subsequent to electronic or system failures, particularly in fuel systems for military vehicles.
U.S. Pat. No. 5,154,221 to Melnik et al., the entirety of which is hereby incorporated by reference, describes a manual bypass mechanism for an electronic fuel injection device on a military vehicle such as a tank. The mechanism described in the Melnik et al. patent is designed for use in an electronically controlled fuel system employing an electronic fuel unit (ECU) for a tank. As described by Melnik et al., the ECU is programmed to initiate several protective modes and reduces fuel flow from the HMU (Hydromechanical Unit) if certain performance irregularities occur in the engine, transmission, or other propulsion system component in order to prevent engine damage.
In one of the protective modes, referred to as “protective mode III”, the flow rate of fuel to the engine is reduced to about 120 lbs./hour, so the engine generates only about 72 hp, or 5 percent of its capacity. The tank must move very slowly, e.g., at 1 mph, to a site where the propulsion system's problem can be analyzed. In a battle or emergency scenario, it may be necessary to drive the tank faster than protective mode III permits. Further, it is possible that battle damage could cut off electrical power to the ECU and thereby adversely limit fuel flow to the engine.
The mechanism described by Melnik includes a completely mechanical fuel bypass device which routes additional fuel to the engine during protective mode III or during failure of the ECU. The device was a modular, add-on unit that can be installed on existing tanks without disassembly of the hydromechanical units and which can be used without modifying the logic of the ECUs.
However, the present inventors have determined that systems of the background art, including that described in the Melnik et al. patent, suffer from several shortcomings. Specifically, the Melnik device requires a screw-type metering valve/metering shaft for controlling fuel flow between a zero-flow position to a fully open position. In addition, the systems of the background art fail to include adequate consideration for protecting against engine overspeed and high temperatures when fuel control is shifted to the manual bypass device.